1. Field of the Invention
The present invention relates to a substrate cleaning method for performing scrub cleaning of a surface of a substrate, such as a semiconductor wafer, with a long cylindrical roll cleaning member by rotating the substrate and the roll cleaning member each in one direction while keeping the roll cleaning member in contact with the surface of the substrate in the presence of a cleaning liquid. The substrate cleaning method according to the present invention can be applied to cleaning of a surface of a semiconductor wafer, or to cleaning of a surface of a substrate in the manufacturing of an LCD (liquid crystal display) device, a PDP (plasma display panel) device, a CMOS image sensor, etc.
2. Description of the Related Art
As semiconductor devices are becoming finer these days, cleaning of various films, made of materials having different physical properties and formed on a substrate, is widely practiced. For example, in a damascene interconnect forming process for forming interconnects by filling a metal into interconnect trenches formed in an insulating film on the substrate surface, an extra metal on the substrate surface is polished away by chemical mechanical polishing (CMP) after the formation of damascene interconnects. A plurality of films such as a metal film, a barrier film and an insulating film, having different water wetting properties, are exposed on the substrate surface after CMP.
A residue of a slurry (slurry residue) that has been used in CMP, metal polishing debris and the like exist on the substrate surface having the exposed films such as a metal film, a barrier film and an insulating film by CMP. If cleaning of the substrate surface is insufficient and the residues remain on the substrate surface, the residues on the substrate surface may cause reliability problems such as the occurrence of leak from a residue portion, poor adhesion, etc. It is therefore necessary to clean the substrate surface, with a high degree of cleanliness, on which the plurality of films such as a metal film, a barrier film and an insulating film, having different water wetting properties, are exposed.
As a cleaning method for cleaning a substrate surface after CMP, there has been known a scrub cleaning method for cleaning a surface of a substrate, such as a semiconductor wafer, with a long cylindrical roll cleaning member (roll sponge or roll brush) by rotating the substrate and the roll cleaning member each in one direction while keeping the roll cleaning member in contact with the surface of the substrate in the presence of a cleaning liquid.
FIG. 1 of the accompanying drawings illustrates the manner in which a surface of a substrate is scrub-cleaned by a roll cleaning member according to the related art. As shown in FIG. 1, a roll cleaning member R has a length slightly larger than the diameter of a substrate W, and is disposed in such a position that the rotational axis O1 of the roll cleaning member R is perpendicular to the rotational axis O2 of the substrate W at the center of the longitudinal direction of the roll cleaning member R, and that the roll cleaning member R and the substrate W are held in contact with each other. While a cleaning liquid is supplied to the surface of the substrate W from a cleaning liquid supply nozzle N, the roll cleaning member R which is rotating about its rotational axis O1 is brought into contact with the surface of the substrate W which is rotating about its rotational axis O2 over the entire length in the diametrical direction of the substrate W, and the surface of the substrate W is rubbed with the roll cleaning member R in the presence of the cleaning liquid, thereby cleaning the surface of the substrate W.
The surface of the substrate W is cleaned in a cleaning area E having a length L where the surface of the substrate W and the roll cleaning member R are brought into contact with each other. The cleaning area E is divided into two areas, one on each side of the rotational axis O2 of the substrate W, i.e., an inverse-direction cleaning area E1 having a length Li where the substrate W and the roll cleaning member R are rotated in opposite directions at a relatively high relative rotational velocity, and a forward-direction cleaning area E2 having a length Lf where the substrate W and the roll cleaning member R are rotated in the same direction at a relatively low relative rotational velocity. It is desirable to supply the cleaning liquid efficiently to the cleaning area E including the inverse-direction cleaning area E1 and the forward-direction cleaning area E2.
As shown in FIG. 1, it is assumed that the surface of the substrate W is divided into a left area WL disposed on the left side of the cleaning area E as viewed from above and a right area WR disposed on the right side of the cleaning area E as viewed from above. When the substrate W is rotated in a clockwise direction about the rotational axis O2 as viewed from above and the roll cleaning member R that is disposed over the substrate W is rotated in a clockwise direction about the rotational axis O1 as viewed from its left end, the cleaning liquid supply nozzle N is generally positioned to supply the cleaning liquid to the right area WR. Thus, the cleaning liquid that has been supplied to and held on the substrate W is initially supplied by rotation of the substrate W to the forward-direction cleaning area E2 where the substrate W and the roll cleaning member R are rotated in the same direction. In the forward-direction cleaning area E2, the moving direction of the cleaning liquid on the substrate W and the rotation direction of the roll cleaning member R are in the same direction (forward-direction). Therefore, while the roll cleaning member R rolls the cleaning liquid on the substrate W therearound, the roll cleaning member R conducts physical contact cleaning. After leaving the forward-direction cleaning area E2, the cleaning liquid on the substrate W is supplied by rotation of the substrate W to the inverse-direction cleaning area E1 where the roll cleaning member R conducts subsequent physical contact cleaning.
Japanese Laid-Open Patent Publication Nos. 2010-278103 and 2010-74191 disclose a scrub cleaning apparatus for performing scrub cleaning of a surface of a substrate with a roll cleaning member (roll brush or roll sponge) by rotating the substrate and the roll cleaning member while keeping the roll cleaning member in contact with the surface of the substrate in the presence of a cleaning liquid. In such a scrub cleaning apparatus, as the substrate makes one revolution on its own axis, the cleaning liquid is supplied to a forward-direction cleaning area and an inverse-direction cleaning area. Japanese Laid-Open Patent Publication Nos. 2003-77876 and 9-69502 also disclose a scrub cleaning apparatus for performing scrub cleaning of a substrate with a roll cleaning member (roll brush or roll sponge) by rotating the substrate and the roll cleaning member while keeping the roll cleaning member in contact with the surface of the substrate in the presence of a cleaning liquid. In such a scrub cleaning apparatus, the cleaning liquid is supplied to the surface of the substrate on opposite sides of the roll cleaning member.
In the forward-direction cleaning area where the relative rotational velocity between the substrate and the roll cleaning member is relatively low, only low physical cleaning capability can be obtained. In the inverse-direction cleaning area where the relative rotational velocity between the substrate and the roll cleaning member is relatively high, high physical cleaning capability can be obtained. As shown in FIG. 1, in the case where the cleaning liquid supply nozzle N is positioned at the right area WR of the substrate W, as the substrate W and the roll cleaning member R rotate, the cleaning liquid that has been supplied from the cleaning liquid supply nozzle N to and held on the substrate W is pushed by the roll cleaning member R and is discharged from the forward-direction cleaning area E2 where the roll cleaning member R rotates in the same direction as the moving direction of the cleaning liquid carried by rotation of the substrate W, and is then fed smoothly into the inverse-direction cleaning area E1 positioned downstream of the forward-direction cleaning area E2. However, the cleaning liquid that has been discharged from the forward-direction cleaning area E2 has its cleaning capability lowered because it has already been used to clean the substrate W. Further, the cleaning liquid having such lowered cleaning capability is carried by horizontal rotation of the substrate W, and reaches the inverse-direction cleaning area E1 while it is discharged to the outside of the substrate W under centrifugal forces generated by rotation of the substrate W. Thus, an amount of the cleaning liquid which reaches the inverse-direction cleaning area E1 decreases significantly.
Thus, it is considered that the cleaning liquid is supplied in a large amount to the inverse-direction cleaning area having high physical cleaning capability, and the cleaning liquid that has been used to clean the substrate W in the inverse-direction cleaning area is then supplied to the forward-direction cleaning area having low physical cleaning capability for cyclic usage, thereby obtaining a high comprehensive cleaning performance.
The forward-direction cleaning area includes a region wherein the relative rotational velocity between the substrate W and the roll cleaning member R is zero under certain cleaning conditions including dimensions and rotational speeds of the roll cleaning member and the substrate. In such a region and surrounding regions, the roll cleaning member is merely pressed or stamped against the substrate without relative movement therebetween. Consequently, the surface of the substrate in those regions may be contaminated back by contact with the roll cleaning member. It is required to effectively clean the surface of the substrate thus contaminated back.
Japanese Laid-Open Patent Publication No. 2010-278103 discloses a scrub cleaning apparatus for cleaning a thin substrate having a relatively large diameter. The scrub cleaning apparatus in the Japanese Laid-Open Patent Publication No. 2010-278103 is configured to prevent insufficient cleaning at a central part of the substrate from occurring due to a warp of the substrate caused by a cleaning liquid which has been supplied to the central part of the substrate and accumulated thereon while the substrate rotates at a low rotational speed. Japanese Laid-Open Patent Publication No. 2010-74191 discloses a scrub cleaning apparatus configured to judge the time for replacement of a roll cleaning member and to avoid contamination of the roll cleaning member.
In the scrub cleaning apparatus disclosed in Japanese Laid-Open Patent Publication Nos. 2010-278103 and 2010-74191, the difference between the physical cleaning capabilities of the forward-direction cleaning area and the inverse-direction cleaning area in the scrub cleaning conducted by the roll cleaning member has not been considered at all. The positions of the cleaning liquid supply nozzles shown in the drawings of Japanese Laid-Open Patent Publication Nos. 2010-278103 and 2010-74191 are considered to have been selected for convenience of illustration, and to have been accidental. Therefore, in. Japanese Laid-Open Patent Publication Nos. 2010-278103 and 2010-74191, there are no descriptions about the relationship between the position of the cleaning liquid supply nozzle and the relative rotational velocity between the substrate and the roll cleaning member.
In the scrub cleaning apparatus disclosed in Japanese Laid-Open Patent Publication Nos. 2003-77876 and 9-69502, because the cleaning liquid is supplied to the surface of the substrate on opposite sides of the roll cleaning member, the amount of cleaning liquid used is comparatively large to be uneconomical, and the apparatus configuration becomes complex. While the roll cleaning member is brought into contact with the substrate lying in the horizontal plane to clean the substrate, the cleaning liquid on the substrate is moved in a circumferential direction of the substrate and discharged therefrom under centrifugal forces generated by rotation of the substrate in the horizontal plane. However, the centrifugal forces are very small or nearly zero in the vicinity of the rotational axis of the substrate, and hence the cleaning liquid is liable to stay stagnant near the rotational axis of the substrate. Therefore, the cleaning liquid is difficult to be replaced with new one, thus lowering the cleaning capability in the vicinity of the rotational axis of the substrate.